Separation of acetylene



July 25, 1961 D. E. GRIFFIN SEPARATION oF ACETYLENE Filed June 24, 1959 nited States Patent C) 2,993,566 SEPARATION OF ACETYLENE Donald E. Griffin, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Filed June 24, 1959, Ser. No. 822,673 6 Claims. (Cl. 18S-115) This invention relates to the manufacture of acetylene. In one aspect, it relates to the dehydration of gases containing acetylene. In another aspect, it relates to an improved process for removing water and heavy acetylenes, such as diacetylene, from gases containing acetylene, using a selective solvent, such as dimethylformamide, and the purification of said solvent. In a further aspect, it relates to the purification of a selective solvent used in a low-temperature process for removing water and heavy acetylenes from gases containing acetylene produced by thermal cracking of low-molecular weight, normally gasesous hydrocarbons.

In recent years, increased demand for commercial acetylene has resulted in considerable eiort directed toward its production by high temperature cracking of low molecular weight, normally gaseous hydrocarbons, such as methane, ethane, propane, butane, natural gas, and the like, in a thermal-cracking furnace. Normally, the hot furnace or reactor eluent gases, containing acetylene and other low molecular weight cracked gases, are subjected to quenching operations to cool the gases and remove undesirable components such as tars, aromatics, carbon black, and other impurities. Following the quenching operation, the quenched gases contain acetylene, higher acetylenes such as diacetylene, water, carbon dioxide, and impurities such as cracked oleiinic gases.

Heretofore, it has been the practice in many acetylene processes to remove the water from the quenched gases by passing the gases through beds of desiccant. While this type of dehydration is generally satisfactory, it has some drawback in that the desiccant has to be periodically regenerated; also some of the cracked olenic gases have a tendency to polymerize on contact With the desiccant, thereby further reducing the useful life of the desiccant beds. i q

The heavy acetylenes, such as diacetylene, have often been removed heretofore from the cracked gases by employing a solvent (e.g., oil) diierent from the solvent.

used in the main acetylene absorption step, thus requiring another item of equipment which adds to the cost of iristallation and operation.

In other processes, the water and heavy acetylenes, such higher purification and recovery process temperatures which necessarily reduce the selectivity of the solvent for acetylene. f

Accordingly, the object of this invention is to provide ice and used in removing diacetylene, and to maintain desired purity of entire solvent stream by means of a single solvent purication step. Further objects and advantages of this invention will become apparent to those skilled in the art from the following discussion, appended claims, and the ow sheet of the accompanying drawing which illustrates the subject invention. It is to be understood that in the following discussion and accompanying drawing only sutiicient pieces of various types of equipment such as vessels, columns, pipes, pumps, heat exchangers, etc., will be discussed and have been shown in the interest of brevity to permit a ready understanding of the subject invention.

Referring now to the ow sheet of the accompanying drawing, a stream 1 from a pyrolysis operation comprising relatively tar-free, quenched, low molecular weight cracked hydrocarbon gases, including acetylene in minor quantities, having a temperature of about 32 to 100 F., and a stream 2 of fresh selective solvent, such as dimethylformamide (abbreviated as DMF in the drawing), are passed via line 3 to a refrigeration unit 4 wherein the gas-liquid mixture is cooled, for example, to a temperature of 2O to 20 F. The amount of selective solvent used at this point will be suicient to dehydrate the gas stream; this will amount to about 0.25 mol percent of the selective solvent used in the main acetylene absorption step, or 0.6 to 2 mols of solvent per mol of water in the gas stream 1. This selective solvent 2 will preferentially absorb the water present in the gas stream 1. The cooled gas-liquid mixture is passed via line 3 into a gas-liquid separation zone 5, such as a knockout drum, wherein the wetfsolvent having substantially all the water absorbed therein is separated from the gas stream. The wet solvent bottoms are withdrawn from knockout drum 5 via line 6, and the dehydrated gas stream is taken oi as overhead via line 7. The dehydrated gas stream is introduced at the lower end of an absorption tower 8 wherein substantially all of the diacetylene, and minor amounts of other low molecular weight higher acetylenes, such as vinylacetylene, are preferentially absorbed and removed. The absorption of the diacetylene in absorption tower 8 is accomplished by contacting the gas stream with acetylene rich selective solvent which is supplied to the upper portion of the absorption tower via line 9.

l The amount of the rich solvent used at this point will be sutcient to remove substantially all of the diacetylene from 4the dehydrated gas stream; generally this will amount to about 1.40 mol percent of the total acetylene rich solvent, or 3 to 20 mols of the rich solvent per mol of diacetylene in the dehydrated gas stream, 'Y

The absorption tower 8 preferably contains contact surface material such as batidos, rings, beads, etc., to

cause intimate Contact of the gases fed thereto with the rich selective solvent. Since water has'been removed from the gas, this absorption step can be carried out at relatively lowQtemperature, eg., -20 to,20 F., and

an improved process for the puriiication of low molecular Weight cracked gases, such as acetylene, obtained from a Another object is to dehydrate cracked gases containing low molecular gases.

thermal-cracking operation.

such as acetylene, and removing heavier acetylenes, such as diacetylene, therefrom by employing a minor amount of the same selective solvent used in the main acetylene absorption step. Another object is to dehydrate relatively tar-free, low molecular weightcracked gases early in the purication train. Another object is lto remove heavy acetylenes, such as hazardous diacetylene,V from low molecular weight cracked gases early in the puriiication train. Another object is to purify the selective solvent used in dehydrating low molecular weight cracked gases i at atmospheric or slightly superatmospheric pressure, e.g.

i 14.7 toV 50 p.s.i.a.

The dehydrated, diacetylene-free gas stream, containing substantially all of the acetylene, is removed from absorption tower 8 as overhead via line 11 and passed to the lower end of an acetylene absorption tower 12, which can contain suitable contact surface material, wherein the gas stream is contacted with fresh selective solvent supplied to the upper end of absorber 12 via line 13, the non-absorbed residue gas being withdrawn as overhead from the top of the tower via line. 14. The acetylene, and minor amounts of heavier acetylenes,'.ab' sorbed in the solvent areremoved as bottoms via'line 16 and pumped to the upper end of a carbon dioxide stripping tower 17, a small portion of the rich solvent bottoms being pumped via line 9 to the upper end of the diacetylene absorber 8. Heating means 18 disposed in the lower end of the carbon dioxide stripper causes strippingof carbon dioxide from'the acetylene-rich` sol- Small amount of acetylene absorbed in the solvent bottoms removed from diacetylene absorber 8 can be recovered in substantial quantities from the bottoms by adding suicient water to displace the acetylene from the vent mixture, the CO2-residue gas being withdrawn as 5 solvent mixture. Y overhead viav line 19 and passed back to acetylene ab- The wet solvent withdrawn from knockout drinn 5 sorber. 12. The carbon dioxide Stripper17 Can be Opervia line 6 isY combined with the diacetylene rich solvent ated at suitable temperature and pressure; for, example, bottoms in line 36 from Hush drum 33 and also comthe lower end of the stripper can be operated at a tcmbined with small' amount of lean solvent withdrawn from perature 218 F., and the upper` end operated at a tem-Y 10 the acetylene stripper 22 via lines 24, 23. This comperature. of 140 F- and 20 p-Si-a- The acetylene-rich brood steam is conveyed via une 35. and heated by hout solvent is withdrawn as bottom from the lower end Of exchanger 37, e.g., to a temperature of 100 to 200 F., Stripper 17 and iS pumped Via line 21 to the upper end and introduced intermediate the ends of a solvent rerun of an acetylene stripper 22 wherein acetylene is stripped orA recovery column 38, from the Solvent and ConveYefl 3S overhead Violine 23 l5 The rerun column 38 can contain suitable liquid-gas t Suitable absorption equipment for the removal of contacting material, such as Rashig rings, bubble or valve hee-vier aCetYleneS therefrom- The acetylene-free lean trays, and the like, and this rerun` column is operated so Solvent, Containing Some heavy aeetYleneS aS impurities, as to'have a temperature gradient; for example, the lower iS-WithdraW11 3S VbOttOlnS from Stripper 22" Via line 24,' end of the rerun column 38 can be operated at a temperaPortion of this Stream being recycled via line 25, having 20 ature about the bubble point` ofthe. kettle product, e.g., en external reholler means z7 associated therewith, to 300 to 400 F., yand the upper endV operated at the dew the stripper. The acetylene stripper 22 can be operated point of the residue gas, erg., 80 to 150 F., this rerun at Suitable temperatures and pressures, for eXample, the column being preferably operated at atmospheric preslOWef end 0f the Stripper een be opereted at e tempera' sure. An inert gas, such as methane, is introduced via tllfe 0f.326 Fo and the upper end Operated at e tempera' 25 line 39 at an intermediate level in rerun' column 38, this ture of 250 and 20 p-S-ii- The maior portion of the inert gas aiding in stripping the diacetylene by decreaslean Vsolvent bottoms is pumped via line 26. to a solvent ing its partial pressure.. Other. inert gases which can be Surge tank 30, from Which the maior portion iS pumped usedin aiding the stripping include` nitrogen, natural gas, "itl line 13 to the upper end o the acetylene absorber residue gas from the acetylene absorber, or the like. The 12a A minor proportion of the lean Solvent from Stripper 30 small amount of solvent which is in the overhead gas can 2z iS also pumped Vie line 28 for mixture With other Sol' be-contactedrwith Water supplied via line 41 to the upper vent prOCeSSStreamS So aS to Control and maintain the end of the towerthe fuel gas overhead, containing water p lllity 0f theSeleCtive Solvent uSed in thel proeeSS- ThiS vapor and diacetylene, being withdrawn as overhead via minor amount of lean solvent will generally be about 0.32, line- 42. m01 percent of the lean Solvent Sent to Surge tank 30, 35Y The purified or fresh solvent vapor is Withdrawn from or 0.5 to 4 Weight percent of the selective solvent used the bottom portion of the reruncolumn 38 via line 43 and in the main acetylene abSorptiOn Step- Y this solvent vapor is cooled Aby means of cooling means Purication of the solvent will now be discussed, refer- 44andl conveyed to -a solventV accumulator tank 46,V the ence being made to the diacetylene absorber 8. The cooled, condensed and puried solvent being pumped bottoms from this absorber 8, Comprising Solvent containfrom the accumulator tothe so1vent surge tank 30 via ing diacetylene, some heavy acetylenes, a small amount line 47.A The'kettle; product from the solvent rerun colof acetylene, and water, is removed as bottoms via line umn 38 is withdrawn via line 4S, having Van external re- 31 and pumped to a heat exchanger 32 whereby the botboiler means 49 associated therewith, and recycled to the toms are heated at a temperature sutlcient to enable the bottom of the tower. Any accumulation of heavy acetylsmall amount of acetylene to Ibe flashedffrom the bottoms enes can be Withdrawnperiodically via line 51. Without at the same time flashing any substantial amount 45 The following material b-alance further illustrates subof the heavier acetylenes dissolved in the. solvent; for exjectinvention.

TABLEi I Material balance-mals per hour Stream Component ample, the bottoms pumped fromabsorber 8 via line V3.1 areheated; to a temperature within the range of' 120 toV Vv180", F., preferably aboutA 1583,13. The heated bottoms are; then flashed irr'flash drum` 33, the flash drumbeing operated ,at atmospheric orslightly superatmospheric 'pres- Y150v F. "The: acetylene containing overheardris passed b'acle tothelower endof the diacetylene absorben 8 via line :34, and the diacetylene; richvsolvent-'bottoms Aremoved YVarious 'modifications andaltenations` of the invention will become .apparent to those 'skilledin the art without departing fronnthe scopeand spirit ofvthis invention, and it' should beV understoodthat the foregoing discussionV and i y accompanying'drawing vare not tobeconstrued so as to sur' e;^e;g.,14.7 to SQ p.s.i.a., andV at a temperatureof'about Y i u unduly limit this'Y invention.Y

-'l`. In -a v process fori recoverying acetylene from l a gas streamfco'ntaining-'the same andV water, diacetylene, and

' Y from the ash drum 33 vialine 36; Alternatively, the 75 heavier acetylenes, which' comprises contacting said gas stream with a first stream of lean selective solvent to dehydrate the same, separating the resulting wet solvent from the resulting dehydrated gas stream, contacting the latter With acetylene-rich selective solvent to absorb diacetylene and part of said heavier acetylenes from said dehydrated gas stream, separating the resulting diacetylene-rich solvent from the resulting diacetylene-free gas stream, contacting the latter with a second stream of lean selective solvent to absorb acetylene and the remainder of said heavier acetylenes therefrom, stripping the resulting acetylene-rich solvent to obtain acetylene and heavy acetylenes and a third stream of lean solvent, combining a minor portion of said third stream of lean solvent with said wet solvent and said diacetylene-rich solvent, heating the combined solvent stream, and stripping the heated combined solvent stream to remove Water, diacetylene, and heavier acetylenes from said solvent.

2. In a process for recovering acetylene from a gas stream containing the same and water, diacetylene, and heavier acetylenes, which comprises contacting said gas stream with a first stream of lean selective solvent to dehydrate the same, separating the resulting Wet solvent from the resulting dehydrated gas stream, contacting the latter with acetylene-rich selective solvent to absorb diacetylene and part of said heavier acetylenes from said dehydrated gas stream, separating the resulting diacetylene-rich solvent from the resulting diacetylene-free gas stream, contacting the latter with a second stream of lean selective solvent to absorb acetylene and the remainder of said heavier acetylenes therefrom, stripping the resulting acetylene-rich solvent to obtain acetylene and heavy acetylenes, and a third stream of lean solvent, combining a minor portion of said third stream of lean solvent With said wet solvent and said diacetylene-rich solvent, heating the combined solvent stream, stripping the heated combined solvent stream to remove water, diacetylene, and heavier acetylenes from said solvent, and combining the resulting fourth stream of lean solvent With a maior portion of said third stream of lean selective solvent.

3. Ihe process according to claim l wherein said selective solvent is dimethylformamide.

4. In a process for recovering acetylene from a gas stream containing the same and Water, diacetylene, and heavier acetylenes, which comprises contacting said gas stream with a rst stream of lean selective solvent to dehydrate the same, separating the resulting wet solvent from the resulting dehydrated gas stream, contacting the latter with `acetylene-rich selective solvent to absorb diacetylene and part of said heavier acetylenes from said dehydrated gas stream, utilizing a minor portion of the resulting acetylene-rich solvent in said diacetylene absorption step, separating the resulting diacetylene-rich solvent from the resulting diacetylene-free gas stream, contacting the latter with a second stream of lean selective solvent to absorb acetylene and the remainder of said heavier acetylenes therefrom, stripping the major portion of said resulting acetylene-rich solvent to obtain acetylene and heavy acetylenes, and a third stream of lean solvent, combining a minor portion of said third stream of lean solvent with said Wet solvent and said diacetylene-rich solvent, heating the combined solvent stream, and stripping the heated combined solvent stream to remove water, diacetylene, and heavier acetylenes from said solvent.

5. In a process for recovering acetylene from a gas stream containing the same and water, diacetylene, and heavier acetylenes, which comprises contacting said gas stream with a first stream of lean selective solvent to dehydrate the same, separating the resulting wet solvent from the resulting dehydrated gas stream, contacting the latter With acetylene-rich selective solvent to absorb diacetylene yand part of said heavier -acetylenes from said dehydrated gas stream, utilizing a minor portion of the resulting acetylene rich solvent in said diacetylene absorption step, heating said diacetylene rich solvent and hashing the same, passing the resulting acetylene overhead back to said diacetylene absorption step, contacting the latter with a second stream of lean selective solvent to absorb acetylene and the remainder of said heavier acetylenes therefrom, stripping the resulting acetylenerich solvent to obtain acetylene and heavy acetylenes, and a third stream of lean solvent, combining a minor portion of said third stream of lean solvent with said wet solvent and said diacetylene-rich solvent, heating the combined solvent stream, and stripping the heated combined solvent stream to remove water, diacetylene, and heavier acetylenes from said solvent.

6. In a process for recovering acetylene from a gas stream containing the same and Water, carbon dioxide, diacetylene, and heavier acetylenes, which comprises contacting said gas stream with a iirst stream of lean selective solvent to dehydrate the same, separating the resulting wet solvent from the resulting dehydrated gas stream, contacting the latter with acetylene-rich selective solvent to absorb diacetylene and part of said heavier acetylenes from said dehydrated gas stream, utilizing a minor portion of the resulting acetylene-rich solvent in said diacetylene absorption step, separating the resulting diacetylene-rich solvent from the resulting diacetyleneree gas stream, contacting the latter with a second stream of lean selective solvent to absorb acetylene and the remainder of said heavier acetylenes therefrom, stripping the carbon dioxide from the major portion of said resulting acetylene rich solvent, stripping said major portion of said resulting acetylene-rich solvent to obtain acetylene and heavy acetylenes, and a third stream of lean solvent, combining a minor portion of said third stream of lean solvent with said wet solvent and said diacetylene-rich solvent, heating the combined solvent stream, and stripping the heated combined solvent stream to remove Water, diacetylene, and heavier acetylenes from said solvent.

References Cited in the iile of this patent UNITED STATES PATENTS 2,891,633 Morro et al Iuner23, 1959 

